In cloud computing, a plurality of virtual machines are provided by a virtualization base (called “hypervisor” below) on a physical machine (information processing device) in a data center, and a service system is constructed with the provided virtual machines. The terminal device of a user who is using the service system uses the service system by accessing the virtual machine via the network. A user of a cloud computing service is able to construct a desired service system by providing the needed virtual machines on physical machines, and is able to construct the desired service system flexibly, while making effective use of the hardware resources of the physical machines.
In the cloud computing, it is possible to make efficient use of the hardware of the physical machines by concentrating specific virtual machines on the physical machine, and so on, and therefore energy savings and resource savings can be made. For example, the hypervisor shares the CPU resources between a plurality of virtual machines, and changes the allocation of the CPU to a virtual machine which needs the CPU, from a virtual machine that is not using the CPU. Furthermore, with regard to the memory resources, the hypervisor releases the memory by, for instance, moving unneeded and non-urgent data in the memory, to an external storage device, and changing the allocation to a virtual machine which needs the memory.
In recent years, in order to make effective use of the limited hardware resources of physical machines, it has been proposed that resources, such as the CPU and memory, be released dynamically by suspending or temporarily halting (pausing) the virtual machines which are in an idle state. In this case, the hypervisor allocates the released CPU or memory to another virtual machine which is in an active state. When the user starts to use the virtual machine again, it is needed to resume the suspended or paused virtual machine, return the released resources to their original state and restore the virtual machine to a normal operating state. Japanese Patent Application Publication No. 2010-224914 discloses suspending and resuming a virtual machine.
Here, suspending a virtual machine involves releasing the CPU or memory, in contrast to a case such as dynamic suspension of the application or OS level, where the CPU or memory is not released.